Abstract

The structure of the benthos (macrofauna, megafauna, macroflora and microflora) was investigated in a bay receiving effluents (St Mary Bay, Nouméa, New Caledonia). The study comprised 10 stations situated in the intertidal and in the subtidal zone. The samples were obtained using SCUBA (subtidal stations) or a spade (intertidal stations). Over a surface of 4,8 m2 266 macrofaunal species were identified. The polychaetes were the most abundant group both with regard to the number of species (97) and the number of specimens. Analysis of the density data of the macrofauna revealed a distinction between the communities of the intertidal and the subtidal zone. The environmental parameters indicated that the zone near the primary sewer is subject to eutrophication. This induces an important development of algae of the genus 'Ulva' and the occurrence of small sized polychaetes of the indicator family Capitellidae. In terms of density and biomass, the Eunicidae dominate, but their presence all over the bay does not allow us to identify it as an indicator of an anthropogenic influence. At the scale of the bay, the influence of the eutrophication is difficult to distinguish, because of the heterogeneity of the substrates. We have demonstrated an increase of macrofaunal diversity as a function of the distance from the sewer. The macrobenthic biomass of the subtidale zone was low compared to values formerly calculated for the south-west lagoon. Biomass varies with the substrate type. The trophic structure was charactensed by filter feeders in the intertidal zone and deposit feeders in the subtidal zone.